The relaxation behaviour of strenght and fracture toughness of amorphous metal-metalloid alloys

The effect of an annealing treatment on crack and fracture kinetics and on mechanical properties of Fe₄₀Ni₄₀P₁₀B₆ and Fe₅Co₇₀Si₁₅B₁₀ amorphous ribbons — both pure and with defined impurities — was investigated by in-situ tensile experiments in SEM. The effect of relaxation processes on tensile strength, microhardness and fracture toughness was analysed. A result of technological interest is the increase of fracture toughness after an annealing treatment in the temperature range T_ann. = (0.55 … 0.6) · T_cryst.. This effect will be enhanced by defined chemical impurities, and it can be well interpreted by a model of fracture toughness variation during a temper process. In this model the deformation behaviour cannot be described within the scope of a homogeneous solid, but it is determined by a relationship between closely localized deformation instabilities.